Live like a baron, with a view of the ocean, on a southern California estate dating back to 1914.

A seven-bedroom, 20-bathroom Montecito mansion, formerly home to one of the city’s “hilltop barons,” is on the market for $40 million by the Beverly Hills-based brokerage, the Agency. Stefan Pommepuy, Santiago Arana and Mauricio Umansky are representing the estate.

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The property is more than 11 acres, and “on the highest hill, closest to the sea,” Mr. Arana said. “Nothing blocks the view” to the ocean, he said, and there are mountains on the other side.

Thursday marks the soft launch event for the listing, and the home is being shown to local agents and buyers now. It will be officially listed in about a month, according to Mr. Arana.

The Peabody Estate, now dubbed Solana, was built in 1914 for Frederick Forrest Peabody, a philanthropist and prominent businessman who helped develop Arrow shirts and collars for apparel company Cluett, Peabody and Co.

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Peabody and four other businessmen were dubbed the “hilltop barons,” both for their stately homes overlooking the water and their general place in society, according to the Santa Barbara County Genealogical Society.

In later years, from 1958 to 1978, the estate was home to a think tank, the Center for the Study of Democratic Institutions, according to Mr. Pommepuy. The organization brought the likes of John F. Kennedy Jr. and Martin Luther King Jr. to the grounds.

Sandi and Bill Nicholson, the former COO of healthcare, home and beauty product manufacturer, Amway, bought the home in 1999 for $5.25 million.

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“It was in an advanced state of disrepair,” Mr. Nicholson said, adding that part of the roof had collapsed and about 100 pigeons had taken up residence inside. “Instead of a restoration, it was a rebuild.”

Keeping the integrity of the property was crucial, Ms. Nicholson said. “But we built it for the next 100 years.”

Behind a gated motor court, the 22,729-square-foot home has three wings. The formal living and entertaining areas are in the east-facing wing, while the northern wing has three guest suites, plus a loggia with mountain views.

The main living area is in the south wing. The open-floor plan includes a chef’s kitchen with stainless steel appliances, a breakfast nook and a family room. Exposed beams, salvaged from a airplane hangar dating to before World War II, according to the listing, unite the space.

The master suite is also in the south wing, featuring an 18th-century French limestone fireplace, an antique crystal chandelier and his-and-her closets and bathrooms, the listing said. Other amenities of the home include a beauty salon, fitness center, wine room, library and reception room paneled in French oak that once belonged to William Randolph Hearst.

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Outside, the extensive gardens were “a real pleasure” to develop, Ms. Nicholson said. An old amphitheater is now a terraced rose garden with more than 500 bushes, she said. There’s also an orchid house, a greenhouse that could be an extra office or art studio and a 19th-century European limestone pergola, plus a pool, turtle pond and several terraces.

This was the sixth restoration project for the couple, whose other projects include a townhouse in Washington, D.C., and a Montana ranch, so they “know how to hide things and how to make new things look old,” Mr. Nicholson said.

The couple, based in Houston, is now looking to spend more time on the water, he added, so they are selling the estate. It was listed in 2014 for $49 million, according to public records, and again in 2016, with a $10 million price cut.

People always ask what’s original in the home, Mr. Nicholson said. There is some original glass, he said, plus five sets of curved doors in the living room that were taken apart—all 400 pieces—resanded and reassembled by a team of local carpenters on the project.

But it’s the site that’s the most impressive original detail of the home, the Nicholsons said.

“It was the greatest site available then,” Mr. Nicholson said. And it still is, with its 360-degree views, ocean breezes and total privacy.

“It’s a site like no other,” Ms. Nicholson added.